The present invention relates to cathode ray storage tubes, and more particularly to a direct viewing bistable storage tube that displays write-through information in a color different from that of stored information.
In certain applications of direct viewing bistable storage CRTs, it is desireable to display, but not store a charge image at the same time another, stored image is being displayed. Such a mode of operation, commonly called "write-through," is used to provide a moving cursor in storage-type computer display terminals, for example. It is also used in interactive graphics terminals to permit selected portions of a display to be moved, changed, or deleted while the rest of the display remains fixed, combining the advantages of refresh and storage graphics.
When operating in write-through mode, stored and unstored charge images are both displayed by a tube's phosphor storage target in the same color (typically green). This may make it difficult to distinguish one from the other, particularly when the stored and write-through images partially overlap. In addition, because write-through images are often of lower brightness than stored images, they may be hard to see if the storage tube has a high background luminance of the same color.
A principal object of the present invention, therefore, is to provide a direct viewing bistable storage tube in which write-through charge images are displayed in a different color than stored charge images.
A related object of the invention is to provide a bistable storage tube in which write-through information is displayed in a color that differs from the background color of the tube's display screen.
Another object of the invention is to provide a bistable storage display screen that produces light images of one color when illuminated by a high energy writing beam, and stored light images of a different color when illuminated only by a low energy flood gun.
Still another object of the invention is to provide a method for displaying stored and write-through charge images on an admixed phosphor bistable storage target in different colors.